ebb (n.)youdaoicibaDictYouDict[ebb 词源字典]
Old English ebba "falling of the tide, low tide," perhaps from Proto-Germanic *af- (cognates: Old Frisian ebba, Old Saxon ebbiunga, Middle Dutch ebbe, Dutch eb, German Ebbe), from PIE root *apo- "off, away" (see apo-). Figurative sense of "decline, decay, gradual diminution" is from late 14c. Ebb-tide is from 1776.[ebb etymology, ebb origin, 英语词源]